Currently, a layered model of a broadband wireless access is illustrated in FIG. 1. The layered model in FIG. 1 includes a physical layer (PHY) and a data link layer (MAC). The data link layer is divided into a service specific convergence sublayer (SSCS or CS), a MAC common part sublayer (MAC CPS) and a security sublayer (SS).
Bandwidth allocation and a scheduling management are implemented at the MAC CPS layer. One of the important characteristics of the broadband wireless access is that it supports various kinds of services. The services are categorized into four categories according to the service data characteristics of the services, and four kinds of service scheduling styles are provided correspondingly as follows:
1. Unsolicited Grant, the service corresponding to the Unsolicited Grant is a Unsolicited Grant Service (UGS).
2. Real-time Polling, corresponding to a Real-time Polling Service (RtPS).
3. Non-real-time Polling, corresponding to a Non-real-time Polling Service (NrtPS).
4. Best Effort, corresponding to a Best Effort Service (BE).
Except the Unsolicited Grant Service, the uplink bandwidth allocations of the other services have to undergo the procedure of the bandwidth request/allocation. The difference of service scheduling categories is mainly embodied in the difference of the sending mode of the bandwidth request.
The service scheduling is that the MAC layer controls the data transmission on the connection according to a different QoS requirement of the service flow corresponding to each connection. Each connection corresponds to one group of the QoS Parameters. The corresponding relationship is shown in Table 1. The QoS Parameters may be managed by the interaction of the flow management messages in the MAC layer, such as DSA, DSC, DSD and DSX-RVD.
TABLE 1UGSrtPSnrtPSBEMaximum sustained service data ratio√√√√Minimum reserved service data ratio√√Maximum delay√√Tolerable dithering√Requesting sending strategy√√√√Service priority√√
For the uplink, a collision may be happened due to supporting multipoint-to-point data sending by the broadband wireless access. For example, several SS/MSSs (subscriber station/mobile subscriber station) send data to BS (base station). Particularly when sending a long data, the collision ratio is high. In order to avoid overmuch collision, the basic mechanism of the uplink channel sending opportunity of the BS is as follows.
The first step: a SS/MSS sends a bandwidth request (BW Request) for the connection to request resource;
The second step: a BS performs an uplink bandwidth allocation according to the bandwidth request, and indicates the usage and the location of each burst for the corresponding connection in an uplink mapping message (UL-MAP);
The third step: the SS/MSS sends the message at the appointed location of the burst on the corresponding connection.
For downlinks, the broadband wireless access supports point-to-multipoint data sending. For example, the BS sends data to several SS/MSSs. In order to distinguish each subscriber in the time-frequency space, the basic mechanism of the downlink channel sending of the BS is as follows.
The first step: the BS performs a downlink scheduling, and indicates the usage and the location of each burst of the corresponding connection in the DL-MAP message.
The second step: a SS/MSS receives the message at the appointed location of the burst on the corresponding connections.
The so-called bandwidth allocation is the procedure that the BS provides the uplink sending opportunity or the opportunity for requesting bandwidth to the subordinate SS/MSS. The procedure is specifically as follows.
After determining the scheduling service categories and the corresponding QoS parameters, the scheduler of the BS may get the throughput and delay requirement of the uplink service, and allocate the sending opportunity or the opportunity for requesting bandwidth at a proper time. The procedure that the BS provides the opportunity for sending bandwidth request to the SS/MSS is called Polling.
Currently, the format of the data transmitting on the physical channel of the broadband wireless access is a frame format. Every frame includes a downlink subframe (DL subframe) and an uplink subframe (UL subframe).
If a TDD (Time Division Duplex) mode is adopted, the downlink subframe is transmitted first, and then the uplink subframe is transmitted subsequently. The OFDM (or SC (Single Carrier)) frame structure of the TDD mode is shown in FIG. 2.
If a FDD (Frequency Division Duplex) mode is adopted, the uplink subframe and the downlink subframe are transmitted simultaneously, and the uplink subframe and the downlink subframe are sent in different frequencies. The downlink subframe is not sent at the same time when the uplink subframe is sent corresponding to the SS of a half duplex FDD mode. The OFDM (or SC) frame structure of the FDD mode is shown in FIG. 3.
No matter the TDD mode or the FDD mode is adopted, one downlink subframe has only one downlink physical layer protocol data unit (DL PHY PDU), and one uplink subframe includes timeslots as following order: a contention slot for initial ranging, a contention slot for bandwidth (BW) requests and one or more uplink physical layer protocol data units (UL PHY PDU). Every UL PHY PDU comes from different subscriber stations (SS).
The downlink PHY PDU start with a preamble which is used for synchronization; and the preamble is followed by FCH (frame control head) burst. The FCH includes a DownLink_Frame_Prefix (DLFP) for appointing the usage and length of one or more downlink bursts closely-following the FCH. A DL-MAP (downlink mapping) message is the first MAC PDU closely-following the FCH if the DL-MAP is sent at the current frame. The UL-MAP closely follows behind the DL-MAP or the DLFP if there is a DL-MAP being sent. They may closely follow behind the DL-MAP and the UL-MAP if the DCD (downlink channel descriptor) message and the UCD (uplink channel descriptor) message are sent in the frames. The DL-MAP message, UL-MAP message, DCD message and UCD message are sent at the location of DL-Burst #1 (the No. 1 downlink burst). The usages and the locations of the other bursts of the downlink subframe are appointed by the DL-MAP, and the usage and location of each burst of the uplink subframe are appointed by the UL-MAP. In the TDD system, a TTG and a RTG may be inserted at the alternation time of the uplink subframe and the downlink subframe for leaving a period time for the BS to complete the alternation of receiving and sending.
In the OFDMA frame structure of the TDD mode shown in FIG. 4, the downlink subframe is transmitted first, and then the uplink subframe is transmitted.
In the OFDMA (or SOFDMA) frame structure of the FDD mode, the uplink subframe and the downlink subframe are sent in different frequencies.
No matter in the frame structure of OFDMA of the TDD mode or of the FDD mode, all the effective subcarriers are categorized into several subcarrier sets, and every subcarrier set is called a subchannel. The PHY burst in the OFDMA is formed by a group of adjacent subchannels and a group of OFDMA symbols. One burst may be allocated to one subscriber (SS) (or a group of subscribers) in the uplink, and may be sent to the SS as a sending unit by the BS in the downlink. An initial access, a periodicity ranging and a bandwidth request of the uplink SS may be performed via a ranging subchannel.
Currently, the broadband wireless access has already proposed a concept of the WiMAX Relay Station (RS). One of the important actions of the RS is to be used as a relay between the BS and the SS/MSS. However, in the system having been set with the relay station, there isn't any scheme for bandwidth allocation and scheduling management of the SS/MSS currently.